1. Field of the Invention
The present invention relates to methods and assemblies connecting semiconductor die to substrates. More particularly, the present invention relates thermal enhancements to heat sink BGA semiconductor packages.
2. Description of the Related Art
Semiconductor wafer fabrication involves a series of processes used to create semiconductor devices and integrated circuits (ICs) in and on a semiconductor wafer surface. Once the integrated circuits on the wafer are completed the wafer is sliced into sections known as die. The die are then typically packaged by mounting on substrates composed of an organic material or laminate to protect them and facilitate their electrical connection to external circuitry.
In BGA (ball grid array) semiconductor packaging, an individual semiconductor die is mounted and electrically connected to a die side of a substrate. The other side of the substrate has an array bonding pads bearing solder balls (a ball grid array (BGA)) by which electrical connection can be made to external circuitry, generally on a printed circuit board (PCB). The die is mounted on the substrate by a epoxy adhesive and electrical pads on the top of the die are then wire bonded to electrical pads on the bonding fingers of the substrate to complete the electrical connection of the die to the substrate.
Heat dissipation is a major factor in integrated circuit reliability. In order to improve heat dissipation from the die in the BGA package, a heat sink is often employed. One design incorporates an exposed drop-in heat sink. A heat sink, generally composed of a conductive metal such as copper is bonded, for example, by soldering or with a thermal adhesive, to the substrate. This drop-in heat sink is configured to at least partially surround the die, without contacting it or the wire bonds between it and the substrate.
The package is then sealed by a mold compound, or encapsulant, in a molding operation. A polymeric mold composition heated above its flow temperature is applied over the die on the substrate and molded to form a housing for the die. The sealed package protects the die from breakage, and hazardous environmental contaminants. The top of the heat sink is exposed at the top of the mold compound to facilitate heat dissipation. Upon further cooling, the mold compound cures and the package is ready for bonding to a PCB.
While such heat sink BGA packages have improved heat dissipation from BGA packages, further enhancements to BGA package heat dissipation would be desirable.